In the early days of the telephone art, use of the telephone was often confined to communications among users within a local geographic area. As a result and over the years, the economies related to accessing a communications system have lead to telephones in a local area usually being interconnected through a central controller, often called a local central office in the art.
As digital computers came upon the scene, another local community of use was discernible. Hence, a central controller is commonly employed for interconnecting various user terminals, or stations. For example, U.S. Pat. No. 3,851,104; entitled "Digital Communications System" and issued Nov. 26, 1974; discloses a time division, multiple access communications system which, under the control of a central terminal, allows an interconnection among a plurality of user terminals by way of a single communications signal channel.
As the digital computer art advanced, parallel advances in the semiconductor art have lead to smaller, relatively inexpensive computers. With the advent of such smaller computers, the technique of central control is being abandoned in favor of a distributed control technique. Also, because of the usually bursty nature of digital computer information, the recent trend has also been toward communications systems having a capability for handling packets of digital information. One such distributed control communications system is disclosed in U.S. Pat. No. 4,063,220; entitled "Multipoint Data Communication System with Collision Detection" and issued Dec. 13, 1977. Such known systems are commonly called Carrier Sense Multiple Access/Collision Detection (CSMA/CD) Systems. Indeed, the '220 patent discloses a communications system in which, when a terminal (or a station, or a source) is to start an intended packet transmission on a communications channel, a phase decoder listens to signals on the channel before transmitting (LBT). Upon detecting the presence of another transmission on the channel (typically by sensing the presence of a carrier signal), the terminal delays the intended transmission until no other transmissions are sensed, i.e., it waits for an idle channel (WIC) (typically by sensing the absence of a carrier signal). When the intended transmission is started, the terminal thereafter listens to signals on the channel, i.e., it listens while transmitting (LWT). If another transmission (or an interference, or a collision) is detected, the intended transmission is terminated and a random number generator is used to schedule a retry after the collision (SRC) by selecting a random interval of time at the completion of which a retransmission of the packet will be attempted.
Known CSMA/CD systems tend to operate at bit rates in the order of ten megabits-per-second and with path electrical cable lengths not exceeding about 2.5 kilometers. Unfortunately, the efficiency of known CSMA/CD systems tends to decrease either, if for a fixed cable length, the bit rate is increased or, if for a fixed bit rate, the cable length is increased. Hence, the art is in need of alternatives for improving system efficiency.